During a driving process of an automobile, lubrication is required to be timely provided between various components using a lubricating oil, to ensure a normal operation of the automobile. If the lubricating oil does not have a good lubricating property, a service life of the automobile may be adversely affected. The lubricating property of the lubricating oil is much associated with a temperature of the lubricating oil, and when the temperature of the lubricating oil is excessively high or excessively low, the lubricating property of the lubricating oil may be adversely influenced.
The temperature of the lubricating oil generally may be not too high when the automobile is normally driving. In the case that the automobile is overloaded or a four-wheel drive mode thereof is set to drive in snow or cross-country, the automobile drives in a state that a hydraulic torque converter slips excessively, which may cause the temperature of a transmission oil to be excessively high, thus losing the lubricating property.
At present, a temperature adjustment function for the transmission oil is mainly realized by a cooling flow passage formed by a thermostatic valve and an external cooling device. In the case that the temperature of a transmission oil passage rises, a heat sensitive material of a thermostatic actuating element expands due to being heated, and a passage for the transmission oil directly flowing back to a gearbox is blocked, thus the oil with a high temperature enters the external cooling device to be cooled and then flows back to the gearbox. On the contrary, in the case that the temperature of the oil is too low, the heat sensitive material of the thermostatic actuating element begins to solidify and shrink, and a piston is reset, the passage for the transmission oil directly flowing back to the gearbox is opened. The oil in the oil passage of the gearbox exchanges heat with a heat generating element of the gearbox during the flowing process, to control the temperature of the oil within an appropriate range.
However, in the practical using process, in the case that the external cooling device is blocked to cause a pressure of the cooling oil to be over high, the problem of a supply shortage of the transmission cooling oil may also be caused.